1. Field of the Invention
The invention relates to an electrical circuit arrangement for controlling the position of a movable object present in a motor vehicle and operated by an electric motor. The electric motor can be operated in one or the other of its directions of rotation through two power switching elements controlled by a control device to adjust the position of the movable object. The control device has command inputs from two manual switching devices, one to command the movable object to move in the xe2x80x9copeningxe2x80x9d direction, and one to command movement in the xe2x80x9cclosingxe2x80x9d direction. When neither manual switching device is activated, the two power switching elements are in turned-off position, and both of the electric motor""s terminals are connected, through the associated outputs of the power switching elements, to the same pole (+/xe2x88x92) of a voltage source of a vehicle electrical system.
2. Background Art
Such switching arrangements are provided to control an electrically operated unit present in a motor vehicle, such as a window or sunroof adjustment system, in a manner corresponding to vehicle requirements and legal provisions.
Such an electrical circuit arrangement, for example, is disclosed by DE 31 35 888 C2. The problem with this circuit arrangement is that if the circuit arrangement should have an error occur in it, such as, if there is an electrical short circuit of part of the circuit, then a so-called xe2x80x9cemergency openingxe2x80x9d is impossible, because the provided components prevent further operation of the electric motor.
This emergency opening is of special significance for motor vehicle window and sunroof adjustment systems operated by electrical motors, e.g. when through carelessness or an accident a motor vehicle ends up in a body of water that is so deep that it is only possible for the passengers to get out through a window or sunroof.
This invention is based on the task of further developing an electrical circuit arrangement of the type mentioned above in such a way that if a short circuit should occur, for example due to immersion in salt water, it is still possible to operate the electric motor, especially in a preferred direction of rotation, namely the direction of rotation causing the movable object to open.
According to the invention, the task is solved by making it possible for the power switching element assigned to moving the movable object in the xe2x80x9copeningxe2x80x9d direction to be activated directly when the user activates the manual switch, thereby bypassing the control device. Simultaneously, the power switching element assigned to moving the movable object in the xe2x80x9cclosingxe2x80x9d direction is blocked or prevented at least during the time that the xe2x80x9copeningxe2x80x9d direction power switching element is activated. Such a design of an electrical circuit arrangement is advantageous in that only a relatively small expense is required to realize such a safety function.